1. Field of the Invention
The invention relates to a method for transmitting service data in telecommunication systems with wireless telecommunication based on a predefined radio interface protocol between telecommunication devices, especially voice data and/or packet data in DECT systems
2. Description of the Related Art
In communication systems comprising a message transmission link between a message source and a message sink, transmitting and receiving devices are used for message processing and transmission. In these devices;    1) the message processing and message transmission can take place in a preferred direction of transmission (simplex operation) or in both directions of transmission (duplex operation),    2) the message processing is analog or digital,    3) the message transmission takes place via a long-distance link wirelessly on the basis of various message transmission methods such as FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access) and/or CDMA (Code Division Multiple Access)—e.g., in accordance with radio standards such as DECT, GSM, WACS or PACS, IS-54, 1S-95, PHS, PDC etc. [cf. IEEE Communications Magazine, January 1995, pages 50 to 57; D. D. Falconer et al: “Time Division Multiple Access Methods for Wireless Personal Communications”] and/or on wires.
“Message” is a generic term which stands both for the meaning (information) and for the physical representation (signal). In spite of the same meaning of a message (i.e, the same information) different signal forms can occur. Thus, for example, a message relating to an object can be transmitted;    (1) in the form of an image,    (2) as a spoken word,    (3) as a written word,    (4) as an encrypted word or image.
In this context, the type of transmission according to (1) through (3) is normally characterized by continuous (analog) signals whereas in the type of transmission according to (4), discontinuous signals (e.g. pulses and digital signals) are usually produced.
On the basis of this general definition of a communication system, the invention relates to a method for transmitting service data in telecommunication systems with wireless telecommunication based on a predefined radio interface protocol between telecommunication devices, especially voice data and/or packet data in DECT systems.
The wireless transmission of service data—e.g., the transmitting and receiving of, for example, voice data and/or packet data over the radio path over relatively large distances—between telecommunication devices, which are spatially separate from one another, are constructed as data sources and data sinks. These can be connected by wireless telecommunication, of a telecommunication system or a telecommunication network (which the scenario for the long-distance transmission of service data) and can take place with the aid of DECT (digital enhanced cordless telecommunication) technology, e.g., according to the publication “Vortrag von A. Elberse, M. Barry, G. Fleming zum Thema: (lecture by A. Elberse, M. Barry, G. Fleming on the subject): “DECT Data Services—DECT in Fixed and Mobile Networks”, Jun. 17/18, 1996, Hotel Sofitel, Paris; pages 1 to 12 and summary” in conjunction with the printed documents (1) “Nachrichtentechnik Elektronik 42” (1992) January/February No. 1, Berlin, DE; U. Pilger “Struktur des DECT-Standards” (structure of the DECT standard), pages 23 to 29; (2) ETSI publication ETS 300175-1 . . . 9, October 1992; (3) Components 31 (1993), Vol. 6, pages 215 to 218; S. Althamrner, D. Brückmann: “Hochoptimierte IC's für DECT-Schnurlostelefone” (highly optimized ICs for DECT cordless telephones); (4) WO 96/38991 (cf. FIGS. 5 and 6 and the respective associated description); (5) Training sheets—Deutsche Telecom, Vol. 48, February 1995, pages 102 to 111; (6): WO 93/21719 (FIG. 1 to 3 and the associated description).
The DECT standard describes a radio access technology for wireless telecommunication in the frequency band from 1880 MHz to 1900 MHz with GFSK (Gaussian frequency shift keying) modulation and a Gaussian filter characteristic of BT=0.5. The DECT technology enables any telecommunication network to be accessed. In addition, the DECT technology supports a multiplicity of different applications and services. The DECT applications comprise, e.g., telecommunication in the home (residential cordless telecommunication), accesses to the public PSTN, ISDN, GSM and/or LAN network, the WLL (wireless local loop) scenario and the CTM (cordless terminal mobility) scenario. The telecommunication services supported are e.g. voice, fax, modem, E-mail, Internet, X.25 services etc.
The DECT standard provides various methods for transmitting service data, especially the protected transmission of voice data and/or packet data (cf. ETSI publication ETS 300175-4, September 1996, chapter 12). It is necessary to divide the service data to be transmitted into data units or data packets which are suitable for transmission (protocol data unit PDU). The protocol data units are adapted to the DECT radio interface protocol, especially to the DECT-related TDMA structure and to the various types of transmission for transmitting service data (cf. ETSI publication ETS 300175-4, September 1996, chapter 12, especially tables 21 to 26). For dividing the service data into the protocol data units, the DECT standard also contains a segmenting mechanism or segmenting procedure, respectively, which allows only a single service data unit (SDU) or possibly only a single fragment of a service data unit to be transmittable in each protocol data unit.
FIG. 1 shows in a basic representation, not true to scale, a service data transmission scenario in which, e.g., three service data units, a first service data unit SDU1, a second service data unit SDU2 and a third service data unit SDU3 are transmitted in accordance with the DECT radio interface protocol in a transmission session for transmitting service data in a DECT system, for example, between a DECT base station used as a transmitter or receiver and a DECT mobile part used as receiver or, transmitter.
For this transmission session, a predetermined number of protocol data units PDU, a first protocol data unit PDU1, a second protocol data unit PDU2, a third protocol data unit PDU3 and a fourth protocol data unit PDU4, which are adapted to the DECT radio interface protocol, especially to the DECT-related TDMA structure and to the various types of transmission for the service data transmission, are available which in each case essentially have a predefined basic structure and which are transmitted successively according to the DECT radio interface protocol. The basic structure of the protocol data unit header PDU1 through PDU4 in each case consists of an introductory part ELT, the so-called PDU header, and information field INF and a data field DAF which are arranged in the specified order in the protocol data units PDU1 through PDU4.
The information field INF contains a first information item IN1 and an extension configured as bit. The extension consists of a second information item 1N2 representing the, value “0” of the bit or of a third information item 1N3 representing the value “1” of the bit. In the text which follows, it will be explained what meaning the individual information items have.
In the specified transmission session, the first service data unit SDU1 is transmitted in the first protocol data unit PDU1, the second service data unit SDU2 is transmitted in the second protocol data unit PDU2 and the third service data unit SDU3 is transmitted in the third protocol data unit PDU3 and the fourth protocol data unit PDU4.
First Protocol Data Unit PDU1
The first service data unit SDU1 is packed into the data field DAF of the first protocol data unit PDU1 by the transmitting telecommunication device (transmitter) of the DECT system. The information field INF containing the information IN1 through IN3 is provided after the header part ELT, so that the receiving telecommunication device (receiver) can evaluate (detect) how large the length of the service data in the data field DAF of the first protocol data unit PDU1 is and whether the service data contained in the data field DAF represent a fragment of the first service data unit SDU1 or the non-end of the first service data unit SDU1 or the complete first service data unit SDU1 or the end of the first service data unit SDU1.
In the present case, the first information item IN1 specifies the length of the first service data unit SDU1 because the first service data unit SDU1 is smaller than the data field DAF of the first protocol data unit PDU1, whereas the second information item 1N2 specifies that the service data contained in the data field DAF represent the complete first service data unit SDU1 and that the end of the first service data unit SDU1 is present. The third information item IN3, which, in principle, is also possible as an extension, is shown in parenthesis in the present case in FIG. 1.
Since the first service data unit SDU1 is smaller than the data field DAF of the first protocol data unit PDU1 and, for the transmission of service data, the condition holds that only one service data unit SDU at least configured as a fragment can be transmitted in each protocol data unit PDU, the shaded area of the data field DAF in FIG. 1 remains unused for the transmission of service data. Ultimately, this has the result that the radio channel capacity available in accordance with the DECT standard is not optimally utilized. In other words, the bandwidth available in the DECT system for the telecommunication is poorly utilized.
In addition, this also results in a deterioration in the transmission rate in the transmission of service data.
This type of service data transmission also leads to the result that, when a service data unit is lost due to transmission disturbances on the radio link between the DECT base station and the DECT mobile part, the resultant greater transmission period cannot be made up or compensated for in the service data transmission (occurrence of lost time). This means that the quantity of service data to be transmitted in the telecommunication device (DECT base station and/or DECT mobile part) is maintained, i.e., not decreased. It is maintained; even though the quality of transmission of the transmission link between the telecommunication devices may only be temporarily poor, and that after another disturbance of the transmission link, an intervention into the data transfer is necessary because the quantity of service data becomes greater and greater.
So that this disadvantageous unwanted phenomenon will not occur in the first place, it is possible, according to the DECT standard, to provide a fixed spare capacity in the protocol data unit for transmitting service data which can be used in the case of transmission losses.
Second Protocol Data Unit PDU2
The second service data unit SDU2 is packed into the data field DAF of the second protocol data unit PDU2 by the transmitting telecommunication device (transmitter) of the DECT system. The formation field INF containing the information items IN1 through IN3 is provided after the header part ELT, so that the receiving telecommunication device (receiver) can evaluate (detect: 1) how large the length of the service data in the data field DAF of the second protocol data unit PDU2 is, and 2) whether the service data contained in the data field DAF represent a) a fragment of the second service data unit SDU2 b) the non-end of the second service data unit SDU2 the complete second service data unit SDU2 or the end of the second service data unit SDU2.
In the present case, the first information item IN1 specifies the service data length of the second service data unit SDU2 because the second service data unit SDU2 is exactly as large as the data field DAF of the second protocol data unit PDU2, whereas the second information item IN2 specifies that the service data contained in the data field DAF represent the complete second service data unit SDU2 and that the end of the second service data unit SDU2 is present. The third information item IN3, which, in principle, is also possible as extension, is represented in “0” in FIG. 1 in the present case.
Since the second service data unit SDU2 is exactly as large as the data field DAF of the second protocol data unit PDU2, the data field DAF of the second protocol data unit PDU2 is completely utilized for the transmission of service data in the present case. The phenomenon described above is in conjunction with the transmission of the first service data unit
SDU1 will therefore not occur in the present case.
Third Protocol Data Unit PDU3 and Fourth Protocol Data Unit PDU4
The third service data unit SDU2 is packed into the data field DAF of the third protocol data unit PDU3 and the fourth protocol data unit PDU4 by the transmitting telecommunication device (transmitter) of the DECT system because the third service data unit SDU3 is larger than the data field DAF of the third protocol data unit PDU3. The third protocol data unit PDU3 is therefore completely filled with a corresponding first fragment FR1 of the third service data unit SDU3, whereas the remainder of the third service data unit SDU3, a second fragment FR2, is packed into the fourth protocol data unit PDU4. The information field INF containing the information items IN1 through IN3 is provided after the header part ELT, so that the receiving telecommunication device (receiver) can evaluate (detect): 1) how large the length of the service data in the data field DAF of the third protocol data unit PDU3 is, and 2) whether the service data contained in the data field DAF represent a) a fragment of the third service data unit SDU3 b) the non-end of the third service data unit SDU3 c) the complete third service data unit SDU3 or d) the end of the third service data unit SDU3.
In the present case, the first information item IN1 in the third protocol data unit PDU3 specifies the service data length of the first fragment, FR1 of the third service data unit SDU2, whereas the third information item IN3 specifies that the service data contained in the data field DAF represent the first fragment FR1 of the third service data unit SDU3 and that the non-end of the third service data unit SDU3 is present. The second information item IN2, which, in principle, is also possible as extension, is shown in parenthesis in FIG. 1 in the present case.
Since the first fragment FR1 of the third service data unit SDU3 is exactly as large as the data field DAF of the third protocol data unit PDU3, the data field DAF of the third protocol data unit PDU3 is completely utilized for the transmission of service data in the present case. The phenomenon described above in conjunction with the transmission of the first service data unit SDU1 will therefore not occur in the present case.
In the fourth protocol data unit PDU4, the first information item IN1 specifies the service data length of the second fragment FR2 of the third service data unit SDU3, whereas the second information item IN2 specifies that the service data contained in the data field DAF represent the second fragment FR2 of the third service data unit SDU3, that the second fragment FR2 represents the remainder of the third service data unit SDU3, and that the end of the third service data unit SDU3 is present. The third information item IN3 which, in principle, is also possible as extension, is shown in parenthesis in FIG. 1 in the present case.
The transmission session is ended at least temporarily with the transmission of the service data units SDU1 through SDU3. This means, e.g., for the downlink, that the DECT base station has no more service data to be transmitted by it to the DECT mobile part at the moment. The DECT mobile part is automatically informed of this non-transmission state (default state) by the following facts, first, according to the predetermined transmission protocol mentioned above—which says that in each protocol data unit, only a single service data unit (SDU) or possibly only a single fragment of a service data unit can be transmitted—only the second fragment FR2 of the third service data unit SDU3 is transmitted in the fourth protocol data unit SDU4, second, no further protocol data unit containing service data is sent to the DECT mobile part by the DECT base station. The above statements for the downlink can also be transferred to the case where the transmission session occurs on the uplink.
Since the second fragment FR2 of the third service data unit SDU3 is smaller than the data field DAF of the fourth protocol data unit PDU4 and, for the transmission of service data, the condition holds that only one service data unit SDU configured at least as a fragment can be transmitted in each protocol data unit PDU, the shaded area of the data field DAF in FIG. 1 remains unused for the transmission of service data. Ultimately, this has the result that the radio channel capacity available in accordance with the DECT standard is not optimally utilized. In other words, the band width available in the DECT system for telecommunication is poorly utilized.
In addition, this also results in a deterioration in the transmission rate in the transmission of service data.
This type of service data transmission also leads to the result that, when a service data unit is lost due to transmission disturbances on the radio link between the DECT base station and the DECT mobile part, the resultant greater transmission period cannot be made up or compensated for in the service data transmission (occurrence of lost time). This means that the quantity of service data to be transmitted in the telecommunication device (DECT base station and/or DECT mobile part) is maintained, i.e., not decreased, even though the quality of transmission of the transmission link between the telecommunication devices may only be temporarily poor, and that after another disturbance of the transmission link, an intervention into the data transfer is necessary because the quantity of service data becomes greater and greater.
European Patent EP 0 708 576 discloses a method for the transmission of payload data in telecommunication systems where the concern is how payload data blocks fashioned as CDMA data packets can be transmitted in ATM cells fashioned as data units. A distinction is made between a multiplex mode and a non-multiplex mode for this transmission. In the non-multiplex mode, a first control octet is contained in the information field of an ATM cell, whereas the first control octet and a second control octet are contained in the information field of the ATM cell in the multiplex mode. The first control octet contains an ACO field with one bit length and a PL field with six bit lengths and a parity field with one bit length. The ACO field indicates whether the first control octet is immediately followed by the second control octet or not. Regardless of whether the first control octet is followed by a second control octet, the PL field indicates the packet length of the CDMA data packet that immediately follows the control octet or the control octets. The parity field serves for error recognition.